[apalrd]

I did some math on the KOP drivetrain, and with a reasonable speed loss constant (about 85%), it will be around 14 ft/sec (about what you got, meebee). That said, it will have relatively poor acceleration and very poor pushing power (it becomes traction limited at about 100 amps per CIM, with 4 CIMs).

About the 2motor vs 4motor thing - You have one 290 watt Fisher-Price and FOUR 250-watt RS550 motors (assuming the 18v 775 is correct, they are about 260 watts at 12v, but at a lower speed and higher torque than the 550's).

I would say that a 4-motor drive is a MUST. You have enough motors to build a very fast mechanism with the FP and BB motors. Remember:
A CIM does ~340 watts
A FP does ~290 watts
A 550 does ~250 watts
The FP last year did ~180 watts.
You can have almost a CIM with a FP. Two 550's gets you a lot more power than a CIM. You probably don't need to liberate the CIM's from your drivetrain, and if you do, at least put two 550's in to replace them (the andymark FP planetary works for 550's too).